A standard utility knife for use with a replaceable flat razor blade has as described in U.S. Pat. No. 4,320,576 an elongated housing having a front end, a longitudinally and longitudinally extending guide open at the front end, a longitudinally extending and transversely open slot, and a longitudinally forwardly directed holding face directed transversely opposite to the slot. A blade holder having a seat for the blade is slidable in the housing between a front use position with the blade projecting longitudinally forward from the guide at the front end and a rear storage position with the blade wholly contained in the housing rearward of the front end. An actuator connected to the holder and exposed at the slot is accessible from outside the housing and operable to shift the blade in the holder between its front and rear positions. A spring braced between the holder and the housing urges the holder and the actuator longitudinally rearward in the housing toward the rear position. Thus it is possible to hold the knife with the blade in the use position by a small force exerted against the actuator, but as soon as the actuator is released the blade snaps back into the housing so that the knife can be safely pocketed.
A knife housing front edge surrounding the blade exit opening of the guide is configured at an angle to a longitudinal blade movement direction, such that the knife housing front edge extends away from the front of the blade toward the back. This way, while cutting, the knife can be held ergonomically at a an obtuse angle relative to the material to be cut, without the knife housing front edge coming in contact with the material to be cut during cutting and impairing the cut.
A similar knife is also illustrated in the comprehensive catalog from Martor KG, Solingen, January 2002, under the heading “Professional Applications” on pages 14 to 21 in various embodiments. On a wide knife housing side, the knife has a longitudinal slot, in which an operating projection is guided that actuates the blade holder. On the end at the blade exit side, the knife housing is set at an obtuse angle relative to the blade movement direction. The knife for left-handed users has the operating projection on the other wide housing side, which means that it is configured mirror-reversed. As a result, two different knives have to be produced for right-handed and left-handed users.
Furthermore, safety knives of this type are offered with varying blade extension lengths depending on the application. Knives with varying blade extension lengths are offered for right-handed and left-handed users, respectively. Consequently, a large number of knives is produced, resulting in high technical and organizational expenses, which affects overall costs.
From the related art, furthermore knives are known, which can be used by right-handed and left-handed users alike. These knives comprise, for example, longitudinal slots on both wide housing sides for an operating projection. The disadvantage with these knives, however, is that the second actuator requires additional manufacturing expenses. In other known systems, such as for example seen in German utility model 82 18 916 and U.S. Pat. No. 6,233,832, the actuator is provided on a rear edge of the blade housing, so that the same knife can be used with equal comfort both by right- and left-handed persons.
Furthermore, knives given sold under the trade name “Cuttex” are known from pages 180 and 181 of the comprehensive catalog of Martor KG, Solingen, January 2002. The knives have a snap-off blade with predetermined break lines. The blade holder is slidable the knife housing and is provided with a snap-fit element that can engage with recesses provided on one side of the housing in the blade movement direction. The engagement of the snap-fit element firmly locks the blade holder and consequently also the blade in a certain locked position, for example the cutting position, in which the blade projects from a blade exit hole. To move the blade to the rear storage position, the snap-fit element must be released from the recess and the blade must be retracted into the housing. Thus this knife is not a safety knife that automatically retracts the blade into the knife housing as soon as the pressure that is applied on the operating projection has eased and/or a cutting reaction force on the blade is removed.
In the knife used with the breakaway blade, the housing front edge of the knife that surrounds the blade exit hole has a first region that is inclined relative to the blade movement direction and extends away from the blade front toward the back. This way, the knife housing cannot come in contact with the material to be cut during cutting and impair the cut. A further second region of the knife housing front edge is inclined parallel to the predetermined cutting lines of the blade segments. This way, a used dull blade segment is easy to break off and a new, unused blade segment can be easily moved into the cutting position. The second region of the knife housing front edge that extends parallel to the predetermined break line, serves as a contact edge for the blade when breaking off the blade. As a result, no tool is required for breaking off the dull blade.